1. Field of the Invention
The invention relates to a method of electrically conductively connecting two superconductive cables which each have at least one superconductive cable surrounded by a dielectric and at least one electrically effective screen arranged above the dielectric, wherein the conductors and screens are at the end of the two cables initially freed of the surrounding layers and are subsequently electrically conductively connected to each other.
2. Description of Related Art
Superconductive cables have been known for a long time in various embodiments. This is basically also true for technology for electrically connecting two superconductive cables. A significant difference of the superconductive cables as compared to conventional cables resides in the fact that the superconductive cables include electrical conductors of a material which, at sufficiently low temperatures, changes over into the superconductive state, with an electrical direct current resistance which is around zero. Suitable superconductive materials are, for example, oxidic materials on the basis of rare earths. Sufficiently low temperatures for changing the material over into the superconductive state are, for example, between 67K and 110K. Suitable cooling agents for all these materials are, for example, nitrogen, helium, neon, and hydrogen or mixtures of these substances. When operating a transmission length for electrical energy with at least one superconductive cable, the superconductive cable is arranged in accordance with known technology in a cryostat which consists of at least one thermally insulated pipe through which a cooling agent suitable for the superconductive material being used is conducted when operating the transmission length, wherein the cooling agent is advantageously one of the cooling agents mentioned above.
In transmission lengths of electrical energy, two or more lengths of a superconductive cable must be connected electrically conductively with one another. This means that the conductors and the screens of the two cables must initially be freed of surrounding layers. After electrically conductively connecting the conductors, the removed layers are in accordance with conventional technology once again applied. This is particularly true for an insulation (dielectric) surrounding the superconductive conductor which is reconstructed, for example, by winding bands of insulation material onto the entire connecting point, including the two conductors. Subsequently, the screens are also electrically conductively connected and if necessary, any layers located above the conductors are restored. This is already very complicated and time consuming in a cable having only one conductor and one screen. In addition, it requires the use of expert personnel. In a cable with two or three concentrically arranged conductors which are insulated relative to each other, as it is disclosed for example in EP 1 552 536 B1, the expenditures are extremely high, especially since it must be insured in this connection that the wall thickness of restored insulation or insulations is at least not significantly greater than the original wall thickness. It is only then that the dimensions of a cryostat surrounding the connecting point can be kept so small that the operation of the transmission length, particularly the flow of the cooling agent, is not impaired by the cryostat.